1. Field of the Invention
The present invention relates to an apparatus for twisting root canal reamer material and a method for constructing the same. More specifically, the present invention concerns an apparatus for manufacturing a root canal reamer having a polygonal cross-section with a greater number of twists and a method of manufacturing same. Further, the present invention discloses a method and apparatus which work-hardens the exterior angular cutting edges of the root canal reamer while the interior remains flexible.
2. Description of the Prior Art
In the construction of conventional root canal reamers, austenitic stainless steel is ground to a very fine cylindrical shape having a triangular or quadrangular cross-section. The root canal reamer is then formed by twisting the stainless steel cylinder. To accomplish this, as shown in FIG. 1, the root portion of the reamer material 1 is held in chuck 2 and pinched with vice-claws 3. The vice-claws are then rotated and move along the reamer material. In order to better hold the sides of the reamer material 1, the vice-claws 3 can be provided with grooves 4. The sides are pinched by the grooves 4 or can be pinched by vice-claws 3 having finely formed tips, as shown in FIG. 3.
It is difficult to assure unified, accurate twisting pitch throughout the reamer. Due to the extreme thinness of the root canal reamer, the prior methods do not provide accurate positioning of the claw 3 on reamer material 1 nor do they assure dimensioned accuracy of groove 4. Where one side of a square reamer has a length of approximately 0.04 mm, the chances are increased that the reamer material will be damaged or simply fail to be twisted. With such fine reamer material the neighboring claws may abut against one another without grasping the reamer material. The claws may also cause scratching or scoring of the reamer material.
A root canal reamer of satisfactory cutting quality should have a positive rake angle as defined later, formed in the twisting process. The resulting root canal reamers are shown in cross-section in FIGS. 4 and 5. As illustrated, the resulting rake angles are all negative. FIG. 4 designates minus 45 degrees. FIG. 5 designates minus 30 degrees (d designates a rotating direction of the reamer and c designates canal wall).
The reamer must be manufactured to avoid breakage or shearing. To accomplish this, the reamer material is work-hardened. The usual work-hardening process compresses the reamer material along each flat face producing uniform work-hardening throughout. This causes flexibility and makes the finished reamer susceptible to breakage. Because the vice-claws must conform to the faces of the reamer material, it is impossible to twist square reamer material in anything but square vice-claws. Furthermore, creating smaller sectional area by compression increases the cost of manufacture while the face-to-vice-claw relationship makes it difficult to produce a cutting face having a concave shape.